Natural births: Better after all?

Mothers who give birth vaginally show significantly greater brain activity in response to their baby’s cry than mothers who have chosen a Cesarean section, new research conducted by a group of researchers at the Yale Child Study Center suggests.

The group, led by Child Study Center assistant professor James Swain, carried out functional MRI scans on six mothers who had delivered naturally and six who had undergone a Cesarean section two to four weeks after their deliveries. When presented with 30-second recordings of their babies crying, the former group showed consistently greater activity in several brain regions — including those scientists believe are implicated in sensory processing, empathy, arousal and motivation — than their counterparts.

“Our results support the theory that variations in delivery conditions … which alter the neuro-hormonal experiences of childbirth might decrease the responsiveness of the human maternal brain,” Swain said.

The study comes out at a time when more women than ever are opting for a Cesarean delivery, and it follows research done in 2002 by the Maternity Center showing that women who have a Cesarean section may initially have more trouble bonding with their babies than those who have natural births.

The National Center for Health Statistics reports that nearly one in three babies in the United States was delivered by Cesarean section in 2006, and the trend line shows a steep hike over the last few years.

“As more women opt to wait until they are older to have children, and by association are more likely to have a Caesarean section delivery, these results are important,” Swain said.

Not only is an aging population contributing to rising rates of Cesarean deliveries, but many more are choosing Cesareans over natural deliveries for non health-related reasons — attracting the media label “too posh to push.”

But Swain said Cesarean sections have been correlated with decreased maternal behaviors in animal models, such as rats and horses, and with increased postnatal depression in humans. But women who elect to have Cesareans, as did the group in the study, have the lowest mortality rate in childbirth.

Both groups of women showed greater brain activity in response to their own babies as compared to a control recording of someone else’s baby — a demonstration that, independent of mode of delivery, parental mood follows specific brain activation patterns, he said.

The research team speculates that its findings may be explained by lower levels of some postpartum hormones in women who have had Cesarean sections. For instance, oxytocin — a chemical naturally released to aid contraction during childbirth — is thought to be involved in maternal behavior and emotional bond formation. Low levels of oxytocin or other postpartum hormones may influence the brain’s ability to process a baby’s cry, Swain said.

Assistant professor of psychology Karyn Frick acknowledged that while this theory would be “her first explanation” for the observed difference between the two groups, there could be other mechanisms at play.

For instance, mothers who deliver naturally have been found to recover physically much more rapidly after childbirth than mothers who have undergone a Cesarean section. Because the women were tested so soon after delivery, she said, the mothers who had undergone Cesarean sections would have still been recovering from surgery.

“Nature’s way is to at least temporarily enhance the mother’s functioning response to her baby’s cry,” she said. “That would clearly be adaptive for both the baby and parent.”

But Marianne LaFrance, professor of psychology and women’s, gender & sexuality studies, said it is important not to make too large a leap from the results of the study.

While scientists know that certain brain areas are correlated with certain behaviors and actions, too little about the brain is currently known for any hard and fast rules, she said.

“One group had different levels of oxygenation in their brains, but that is not necessarily a measure of motivation, empathy, attachment or high-quality bonding,” she said. “There’s a big difference between increased oxygenation in the thalamus or hypothalamus and a translation of those areas into such things as empathy or closeness or bonding.”

Swain’s study was published in the Journal of Child Psychology and Psychiatry yesterday.